Emergency isolation valves (EIVs) are possibly the most important pieces of equipment in any given process due to the function they are tasked with performing. Also commonly referred to as emergency shutdown valves (ESVs), safety shutoff valves (SSVs or SSoVs) or “chopper valves”, EIVs are typically controlled by a separate safety instrumented system (SIS) to isolate the flow into a process. Essentially, they “chop” the flow quickly and securely.
EIVs typically come in two distinct forms. One is a pre-designed catalog part number, using carefully selected off-the-shelf components and designed to meet various industry standards for fuel shutdown service. For instance, in North America most of these types of valve assemblies are designed to meet the requirements of Factory Mutual (FM) Global Class 7400 (fire safe class 7440), or CSA International Standards Specification Z21.21/CSA 6.5 Automated Valves for Gas Appliances and CGA3.9-M94 Automated Safety Shut Off Gas Valves. Several manufacturers offer this type of valve, with some variety of body, trim and seat materials, solenoid coil voltages, and limit switch design.
These valves are designed to reliably shut off liquid or gaseous fuels to fuel-burning equipment such as boilers, furnaces, process heaters and burners. The manufacturers of these valves try to meet the widest range of process and ambient pressure and temperature that is practical. This makes it simple and straightforward for a customer to select a valve and be confident that it will meet both its intended function and the regulatory requirements of their customer, customer’s insurer and local fire inspector.
This type of valve is used for most fuel safety applications in industrial locations. Common applications are fuel safety shutoff of fuel oil and gas to boilers, process heaters and burners in manufacturing plants; and even some boilers, process heaters and burners in refineries and chemical plants, where the fuel being controlled is compatible with the valve design.
There are many advantages to using a pre-designed shutoff valve. Each manufacturer has had to present their products to the standards agency for testing and approval, and any revisions to their products must be re-submitted before they can be labeled as approved. The standards agency regularly inspects the manufacturer’s facilities and reviews their quality procedures. The manufacturer’s literature also provides a clear selection guide that helps a less-experienced buyer select an appropriate valve with confidence. And probably most importantly, the manufacturer assumes most of the risk if the valve were to fail to function properly during an emergency event.
There are also drawbacks to using a pre-designed shutoff valve. First, these valves are designed for “standard” industrial applications, so if the plant where it will be used has a different air supply pressure, control voltage requirements or an unusual regulatory agency or requirement, you may not be able to find a pre-designed valve that will work. Second, these valves are specifically designed for shutting off commonly used fuels, and may not be appropriate for shutting off a flammable process ingredient, as might be found in a refinery or chemical plant. Third, the components of the EIV may not match the approved manufacturer’s list (AML) for this plant, bringing in items that the plant personnel may not be familiar with. And last, these valves must be repaired at a shop approved by the standards agency to retain approval.
Which brings us to the second type of EIV, a valve that is custom-designed for the unique process, environmental and regulatory requirements where it will be used. There are two interlocking parts to this approach. First, a careful analysis of the process requirements needs to be made so components that meet the technical requirements of the application can be selected. Second, the regulatory, safety and insurance requirements of the plant and its owner must be considered before the valve design is finalized and the valve is procured.
This approach is more complex and places more responsibility and liability on the plant owner and/or the consultants they use to select the valve. The individual who does this work will need to determine what industry standards, third-party approvals and reliability levels must be met. That person must then select components that meet them and confirm that the completed design will reliably perform the required shutdown function.
Alternatively, this approach allows one to accommodate extreme process conditions, handle a wider range of process fluids and provide levels of safety and reliability that the pre-designed safety shutoff valves cannot. This method is typically required for applications in refineries and chemical plants where a flammable process fluid, such as petrochemicals, partially refined oil, plant gas, alcohols and other chemical feedstocks must be shut off to prevent damage or injuries in an emergency.
Most pre-engineered safety shutoff valves have soft seats — typically fluoropolymer materials that make designing a tight-shutoff valve easier. However, these materials are usually limited to a maximum temperature of approximately 500° F (260° C). If the process temperature of the fluid exceeds these limits, a valve with metal seats is most likely needed and a custom design will be required.
In addition to severe conditions or unusual fluids, plant owners may identify shutoff requirements that require extremely high levels of reliability. When designing a SIS for a process plant, the components like EIVs will require safety integrity level (SIL) analysis to confirm that they will operate reliably when called on. While the application of SIS systems is beyond the scope of this article, one should be aware that the EIV may be called out to have a SIL2 or SIL3 level of reliability. This SIL level is determined by the expected reliability of each component (valve, actuator, solenoid, limit switch, etc.), and by how often the EIV can be tested to verify it functions properly.
Because many plants are being run two, three or even five years between shutdowns for maintenance, testing of the valve at more frequent intervals is often required to meet the required SIL level. One way to accomplish this is a partial stroke test (PST) device that allows initiating the movement of the valve towards the safe position, confirming it has started to move, and then returning to the operational position before the fuel or process flow can be interrupted, causing a shutdown.
Other strategies to improve reliability include redundant solenoids or limit switches that prevent a single point of failure from causing a nuisance trip that shuts down the process. Actuators may be sized to operate at lower pressures (e.g., size for 40 psig when normal system pressure is 60 psig) so valves will still operate if the air supply system is compromised in an emergency. And many refineries require EIVs to use ANSI 300 valves, with their more robust flange connections and greater wall thickness, even if process conditions might allow ANSI 150 valves.
To document that EIVs will perform as expected, suppliers should provide calculations predicting valve stroke time; actuator torque calculations to show the safety factor of the actuator; and compare maximum actuator torque to the maximum allowable stem torque (MAST) of the valve to confirm the actuator will not damage a stuck valve.
Once the EIV has been designed and assembled, it should be tested to confirm it operates as expected. Many plants require a representative to witness the vendor’s testing to assure themselves these critical safety devices provide the performance that has been promised. This witnessing has begun to be performed remotely, with the customer observing via a webcam, due to the COVID-19 pandemic. However, this practice may continue post-pandemic to allow easier and less expensive confirmation of performance.
EIVs are a critical safety device for fuel-burning equipment and industrial processes that use flammable ingredients. Proper selection is critical for the safety of the workers in the plant, plant equipment and the surrounding communities.
Peter Jessee, P.E. is a Process Application Engineer and Dave Fahlgren is a Customer Service Manager for Valin Corporation, a leading technical solutions provider for the technology, energy, life sciences, natural resources and transportation industries. Valin offers personalized order management, on-site field support, comprehensive training and applied expert engineering services utilizing automation, fluid management, precision measurement, process heating, and filtration products. For more information, please visit www.valin.com.
